This invention relates in general to fiber-optic transmitter arrangements and more specifically to a novel laser temperature controller circuit for a fiber-optic transmitter.
Fiber-optic receivers and transmitters or fiber-optic interface units are used in modern telecommunications and data transmission systems between an optical fiber transmission line and electronic digital equipment. The fiber-optic transmitter receives electrical signals from the electronic equipment representing the data to be transmitted. The transmitter then converts the data to light pulses which are coupled to an optical fiber transmission line. The fiber-optic receiver receives light pulses representing the transmitted data from an optical fiber transmission line and converts the light pulses to electrical signals which are sent to and processed by the electronic digital equipment. These systems work in very high transmission rates from 145 Mbs to 2400 Mbs (Megabits per second).
Transmission of data or other signals along optical fiber transmission lines have advantage in the fact that light rays are almost immune to electromagnetic interference such as sparks, lightening, crosstalk and other interference which may be induced into the transmission line.
Many fiber-optic transmitters use a high output solid state light emitting device or laser diode to produce the light pulses used in the transmission of data. The electrical signals received from the electronic equipment are input into a laser drive circuit which modulates the laser diode producing the light output signals.
The power efficiency of a laser diode is the ratio of optical power output to input power. Both power and quantum efficiency are strongly temperature dependent. A laser diode may exhibit a shift in wavelength equal to a 2.2 A (Angstrom) per degree K (Kelvin). The temperature rise of the laser diode junction during a current pulse, therefore, causes an increase in the wavelength during the pulse.
Further, since the junction temperature rises during each individual current pulse, this would tend to cause a decrease in quantum efficiency as well as the aforementioned wavelength shift. If the temperature of the laser diode is permitted to rise too high during a drive pulse the laser would eventually quench itself. This effect reduces the power efficiency if the pulse length is increased beyond a certain point.
It therefore becomes an object of the present invention to disclose a novel laser temperature controller for monitoring and controlling the operating temperature of a laser diode used in a fiber-optic transmitter.